File dolly.md of Package dolly
DOLLY
=====
A program to clone disks / partitions / data.
Take same amount of time to copy data to one node or to X nodes.
SYNOPSIS
========
dolly \[**-f** config\]
dolly \[**-I** infile\] \[**-O** outfile\|-\] \[**-H** hostlist\]
dolly **-v** **-r** 40 **-S** SERVERIP **-H** IPNODE1,IPNODE2,IPNODE3 **-I** /dev/vdd **-O** /dev/vdd
DESCRIPTION
===========
Dolly is used to clone the installation of one machine to (possibly
many) other machines. It can distribute image-files (even gnu-zipped),
partitions or whole hard disk drives to other partitions or hard disk
drives. As it forms a "virtual TCP ring" to distribute data, it works
best with fast switched networks.
As dolly clones whole partitions block-wise.
OPTIONS
=======
If used without a configuration file following three commanline options must be
set:
**-I** FILE : FILE is used as input file.
**-O** FILE\|- : FILE will be used as output file, if '-' is used as FILE, the
output will printed to stdout.
**-H** HOSTLIST: A comma seperated hostlist, where then the first host of the list
is used as firstclient and the last host as lastclient, like in the
configuration file.
Following other options are:
**-h**
: Prints a short help and exits.
**-V**
: Prints the version number as well as the date of that version and exits.
**-v**
: This switches to verbose mode in which dolly prints out a little
bit more information. This option is recommended if you want to
know what's going on during cloning and it might be helpful during
debugging.
**-s**
: This option specifies the server machine and should only be used
on the master. Dolly will warn you if the config file specifies
another master than the machine on which this option is set.
This option must be secified before the "-f" option!
**-S**
: Same as "-s", but dolly will not warn you if the server's hostname
and the name specified in the config file do not match.
**-R**
: resolve the hostnames to ipv4 addresses
**-6**
: resolve the hostnames to ipv6 addresses
**-q**
: Usually dolly will print a warning when the select() system call
is interrupted by a signal. This option suppresses these warnings.
**-c**
: With this option it is possible to specify the uncompressed size
of a compressed file. It's only needed for performance statistics
at the end of a cloning process and not important if you are not
interested in the statistics.
**-d**
: The "Dummy" option disables all disk accesses. It can be used to
benchmark the throughput of your system (computers, network,
switches). This option must be specified before the "-f" option!
**-t** <seconds>
: When in dummy mode, this option allows to specify how long the
testrun should approximately take. Since the dummy mode is mostly
used for benchmarking purposes and single runs might result in
different speeds (especially with many machines and bad switches
or with small TCP segment sizes), it's more convenient to specify
the run-lenght in seconds, as the benchmark-time becomes more
predictable.
**-f** <config file>
: This option is used to select the config file for this cloning
process. This option makes only sense on the master machine and
the configuration file must exist on the master.
**-o** <logfile>
: This option specifies the logfile. Dolly will write some
statistical information into the logfile. it is mostly
used when benchmarking switches. The format of the lines in the
logfile is as follows:
Trans. data Segsize Clients Time Dataflow Agg. dataflow
[MB] [Byte] [#] [s] [MB/s] [MB/s]
**-a** <timeout>
: Sometimes it might be useful if Dolly would terminate instead of
waiting indefinitely in case something goes wrong. This option
lets you specify this timeout. If dolly could not transfer any
data after <timeout> seconds, then it will simply print an error
message and terminate. This feature might be especially useful for
scripted and automatic installations (such as "CloneSys"), where
you don't want to have dolly-processes hang around if a machine
hangs.
**-n**
: Do not sync() before exit. Thus, dolly will exit sooner, but data
may not make it to disk if power fails soon after dolly exits.
**-u** <size>
: Specify the size of buffers for TCP sockets. Should be a Multiple
of 4K.
**-b** <size>
: Option to specify the TRANSFER_BLOCK_SIZE. Should be a multiple of
the size of buffers for TCP sockets.
**-r** <n>
: Retry to connect to mode <n> times
Configuration file
------------------
One can use either us the appropriate commandline options (-i,-o and -H) or a
configuration file for the cloning process is needed. Its format is strict, but
easy. It contains the following entries (note that the order of the entries is
fix): (The text after "Syntax:" explains the syntax of the entry, the lines
following "EG:" are example lines)
1. The file/partition you want to clone, preceeded by the keywords
"infile" or "compressed infile" in case of a compressed image.
This file or partitions needs to be available on the master only.
Dolly will warn you if you try to use a compressed infile which
does not end with ".gz". The compressed keyword is important so
that the master can inform the clients when they have to use gunzip
before writing a file. The optional keyword "split" after the
filename instructs Dolly to read all files with the given name and
an appended number, separated by an underscore.
Syntax: [compressed] infile <input file or device> [split]
EG: infile /dev/sda10
Will just send the partition /dev/sda10 to all clients.
EG: compressed infile /images/cloneimages/sda10_WinNTRes.gz
Will send the given file compressed to all the clients,
instructing them to uncompress the image before writing it.
EG: infile /images/cloneimages/sda split
Will send all files of the form /images/cloneimages/sda_<number>
in order to the clients.
EG: compressed infile /images/cloneimages/sda.gz split
Will send all files of the form /images/cloneimages/sda.gz_<number>
in order to the clients, instructing them to decompress the
incoming stream before writing it.
2. The file or partition you want to write (usually its a partition,
but you can also write to a file) after the keyword "outfile". This
file needs to be available on the clients only. The optional
keyword "compressed" instructs the server to compress the data
before sending it, so the client will store the data
compressed. The optional keyword "split" after the filename,
followed by a number and a multiplier, instructs the client to
write the data in junks of no more than the given size. This is
useful if the file system on your client does not allow files
greater than a certain size. The files will be stored with the
given namen and an appended "_<number>".
Syntax: [compressed] outfile <output file or device> [split <n>(k|M|G|T)]
EG: outfile /dev/sda10
Will store the incoming data stream to the partition sda10.
EG: compressed outfile /images/cloneimages/sda10_SuSE81.gz
Will store the compressed data stream in the given file.
EG: compressed outfile /images/cloneimages/sda_all.gz split 2G
Will store the incoming compressed data stream in the directory
/images/cloneimages/ in files sda_all.gz_0, sda_all.gz_1 and so on.
-. Instead of the first two entries ("infile" and "outfile") it is
also possible to use the single line "dummy [<MB>]", where <MB> is
the number of Megabytes to transfer in dummy mode. If <MB> is set
to 0, then the clients will just terminate. This is useful when
benchmarking with different options, so the clients can run all the
time. To finally terminate them on all clients, just set dummy to 0.
NOTE: It is probably better to use the newer "-t" switch on the
server to specify the number of seconds the benchmarks should
run. In that case you can leave the <MB> blank.
Syntax: dummy [<MB>]
EG: dummy 128
-. The optional keyword "segsize" is mostly used to benchmark
switches. It specifies the maximal size of TCP segments during the
network transfer. Usually you don't need to specify this option at
all.
Syntax: segsize <TCP_MAXSEG size>
EG: segsize 128
-. With the optional keyword "add" it is possible to add more
interfaces to use. The network traffic is then evenly distributed
across the interfaces. This option is useful if you have for
example two fast ethernet interfaces in your machines: One for
administrative purposes and one for your main application on the
cluster. This option is not so useful if you have multiple
interfaces with different bandwidths. In this case just use the
fastest available.
You have to specify the number of additional interfaces and the
suffixes of thouse interfaces. For example, in a cluster where the
machines are named slave0..slave15 on their default interfaces and
all the machines have a second interface named
slave0-fast..slave15-fast, you should use the line specified below
(EG).
Syntax: add <nr>:<suffix>{:<suffix>}
EG: add 1:-fast
-. The optional keyword "fanout" was mostly used during performance
tests of different network topologies. You barely need it in
practice. Fanout specifies the number of outlinks from the server
and the following machines (except the leafes). A fanout of 1 is a
linear list (the default behaviour of Dolly and usually the
fastest), 2 is a binary tree, 3 is a ternary tree, etc. Dolly
automatically connects all the specified clients with the desired
topology.
Syntax: fanout <fanout>
EG: fannout 1
-. The optional keyword "hypennormal" instructs Dolly to treat the '-'
character in hostnames as any other character. By default the
hyphen is used to separate the base hostnames from the names of the
different interface (e.g. "node12-giga"). You might use this
paramater if your hostnames include a hypen (like e.g. "node-12").
Syntax: hyphennormal
EG: hyphennormal
3. After the keyword "server" follows the hostname of the server (or
master). This is required for the last machine in the ring to be
able to send the end-acknowledge back to the server.
Syntax: server <master machine>
EG: server cluster-master
4. This entry has the keyword "firstclient" followed by the hostname
of the first client in the ring. You should use the hostname of the
machine here, not the name of the interface where you want to
connect.
Syntax: firstclient <name of first machine>
EG: firstclient cluster-1
5. This entry has the keyword "lastclient" followed by the hostname of
the last client in the ring. You should use the hostname of the
machine here, not the name of the interface where you want to
connect.
Syntax: lastclient <name of last machine>
EG: lastclient cluster-9
6. This entry specifies how many clients are in the ring. The keyword
is "clients" followed by the actual number of clients. This number
does not include the master.
Syntax: clients <number of clients>
EG: clients 9
7. The following lines contain the interface-names of the client
machines. The number of machines must match the above number of
clients (see 6.). You should use the name of the interface on
which the machines will receive the data.
Syntax: <name of client 1>
<name of client 2>
[...]
<name of client n>
EG: cluster-1-giga
cluster-2-giga
[...]
cluster-9-giga
8. The last entry in the config file consists of the keyword
"endconfig" and marks the end of the configuration file.
Syntax: endconfig
EG: endconfig
Note on nodes hostnames
------------------------
On some machines (e.g. with very small maintenance installations),
gethostbyname() does not return the hostname (I don't know why). If
you have that problem, you should make sure that the environment
variables MYNODENAME or HOST are set accordingly. Dolly first tries to
get the environment variable MYNODENAME, then HOST, then it tries
gethostbyname(). This feature was introduced in dolly version 0.58.
How it works
============
Setting up or upgrading a cluster of PCs typically leads to the
problem that many machines need the exact same files. There are
different approaches to distribute the setup of one "master" machine
to all the other machines in the cluster. Our approach is not
sophisticated, but simple and fast (at least for fast switched
networks). We send the data around in a "virtual TCP ring" from the
server to all the clients which store tha received data on their local
disks.
One machine is the master and distributes the data to the others. The
master can be a machine of the cluster or some other machine (in the
current version of dolly it should be the same architecture
though). It stores the image of the partition or disk to be cloned or
has the partition on a local disk. The server should be on a fast
switched network (as all the other machines too) for fast cloning.
All other machines are clients. They receive the data from the ring,
store it to the local disk and send it to the next machine in the
ring. It is important to note that all of this happens at the same
time.
The cloning process is depicted in the following two figures. Usually
there are more than two clients, but you get the idea:
+========+ +==========+ +==========+
| Master | | Client 1 | | Client 2 |
+====+===+ +===|======+ +====+=====+
\ | /
\ +===+====+ /
+===+ Switch |=====+
+========+
Cloning process, physical network
+========+ Data +==========+ Data +==========+
| Master |========>| Client 1 |=======>| Client 2 |
+========+ +==========+ +==========+
^ | |
| Data | Data | Data
| V V
+======+ +======+ +======+
| Disk | | Disk | | Disk |
+======+ +======+ +======+
Cloning process, virtual network with TCP connections
We choose this method instead of a multicast scheme because it is
simple to implement, doesn't require the need to write a reliable
multicast protocol and works quite well with existing
technologies. One could also use the master as an NFS server and copy
the data to each client, but this puts quite a high load on the server
and makes it the bottleneck. Furthermore, it would not be possible to
directly clone partitions from one machine to some others without any
filesystem in the partition.
Different cloning possibilities
-------------------------------
There are different possibilities to clone your master machine:
- You already have an image of the partition which you want to clone
on your master (raw or compressed). In this case you need Linux
(some other UNIX might also work, but we haven't tested that yet) on
your master and a Linux on each client.
- You want to clone a partition which is on a local disk of your
master. In this case you need Linux (or probably another UNIX, we
haven't tried that) on your master as well as on all the clients.
You can use any Linux installation as long as it's not the one you
want to clone (i.e. you can not clone the Linux which you are
currently running in. See the warning below).
- You want to clone a whole disk including all the partitions. In this
case you either need a second disk on all machines where your Linux
used for the cloning process runs on (not the one you want to clone)
or you need a small one-floppy-disk-Linux which you boot on all
machines. In the later case you also need dolly on all machines
(copy it to your floppy disk or mount it with NFS) and the
config-file on the master.
WARNING: You can NOT clone an OS which is currently in use. That is why
we have a small second Linux installation on all of our machines
(or a small system that can be booted over the network by PXE),
which we can boot to clone our regular Linux partition.
CHANGES
=======
See CHANGELOG file
EXAMPLE
=======
In this example we assume a cluster of 16 machines, named
node0..node15. We want to clone the partition sda5 from node0 to all
other nodes. The configuration file (let's name it dollytab.cfg)
should then look as follows:
```
infile /dev/sda5
outfile /dev/sda5
server node0
firstclient node1
lastclient node15
clients 15
node1
node2
node3
node4
node5
node6
node7
node8
node9
node10
node11
node12
node13
node14
node15
endconfig
```
Next, we start Dolly on all the clients. No options are required for
the clients (but you might want to add the "-v" option for verbose
progress reports). Finally, Dolly is started on the server as follows:
dolly -v -s -f dollytab.cfg
That's all.
Bibliography
============
Felix Rauch, Christian Kurmann, Thomas M. Stricker: <em>Optimizing the
distribution of large data sets in theory and practice</em>. Concurrency
and Computation: Practice and Experience, volume 14, issue 3, pages
165-181, april 2002. (c) John Wiley & Sons, Ltd.
Maintained by Felix Rauch.
http://www.cs.inf.ethz.ch/~rauch/
Felix Rauch <rauch@inf.ethz.ch>
AUTHORS / CONTRIBUTORS
=======================
Felix Rauch <rauch@inf.ethz.ch>
Antoine Ginies <aginies@suse.com>
Christian Goll <cgoll@suse.com>
